1. Field of the Invention
The present invention relates to a low temperature-fired porcelain having a high dielectric constant εr and to an electronic part using such porcelain.
2. Related Art Statement
In high frequency circuit radio instruments such as cellular phones, top filters, interstage filters, local filters, etc. are used as high frequency circuit filters, and a laminated type dielectric filter is used as an interstage filter.
In order to produce a dielectric-laminated filter, a plurality of green sheets are produced from a powdery ceramic material to constitute a dielectric, and a given electrode pattern is formed on each of the green sheets by printing with a given conductive paste. A laminate is then obtained by laminating the resulting green sheets, and the laminate is fired so that the conductive paste layers and the green sheets are simultaneously fired to densify the laminate.
At that time, a metallic conductor having a low melting point, such as a silver-based conductor, a copper-based conductor or a nickel-based conductor is generally used for the electrode. The melting points are, for example, 1100° C. or lower. Ag has a melting point of about 950 to 960° C. For this reason, the dielectric needs to be sintered at a firing temperature lower than the melting point of the metal constituting the electrode.
The assignee has disclosed a dielectric composition for firing at a low temperature in Japanese patent publication H5-319922A.
It has recently been demanded to further miniaturize electronic parts and thus to further improve the dielectric constant εr of a dielectric porcelain composition. For example, the lower limit of dimensions of a dielectric laminate filter obtainable is 2.0 mm×1.25 mm when the dielectric composition having a dielectric constant of 80. When a dielectric porcelain composition having a dielectric constant of 110 or higher is used, the lower limits of the dimensions of the filter can be reduced to 1.6 mm×0.8 mm.
An object of the present invention is to provide a dielectric composition for firing at a low temperature having a high dielectric constant εr, a high Q value, and a low temperature coefficient τf of resonance frequency.